微生物对混凝土的侵蚀(英文)

微生物侵蚀会导致混凝土的严重破坏,尤其导致了城市污水收集和处理系统的过早破坏,使其需要提前修复。世界范围内的研究结果表明:处于污水和下水道污泥中的混凝土会遭受由硫酸盐、酸、CO2等导致的严重破坏。评述了混凝土处于利于细菌生长和生物降解环境中时的细菌、微生物侵蚀破坏过程。此外还分析了硫酸产生的机理(硫循环)、用于污水管道系统和农用工业的混凝土的受侵蚀破坏机理以及评价混凝土抵抗微生物侵蚀的方法。     

Effect of Nitric Acid “Washing” Procedure on Electrochemical Behavior of Carbon Nanotubes and Glassy Carbon μ-Particles

The electroanalytic performances of glassy carbon paste electrode (GCPE), multi-walled carbon nanotube (MWCNT)-GCPE and double-walled carbon nanotube (DWCNT)-GCPE, which include HNO₃ washed/unwashed materials, were compared by monitoring cyclic voltammograms of potassium ferricyanide and catechol. Electrodes were prepared by introducing proper amount of DWCNT and MWCNT into GCPE. First untreated materials (DWCNT, MWCNT, GC μ-particles) were used in the electrodes and then HNO₃-treated materials were utilized for comparing difference in electrochemical performances. The effect of treatment procedure was also examined by applying Raman spectroscopy to treated and untreated materials. Moreover, TEM images were obtained for further investigation of MWCNT and DWCNT.     

Comparative seismic design optimization of spatial steel dome structures through three recent metaheuristic algorithms

Steel dome structures, with their striking structural forms, take a place among the impressive and aesthetic load bearing systems featuring large internal spaces without internal columns. In this paper, the seismic design optimization of spatial steel dome structures is achieved through three recent metaheuristic algorithms that are water strider (WS), grey wolf (GW), and brain storm optimization (BSO). The structural elements of the domes are treated as design variables collected in member groups. The structural stress and stability limitations are enforced by ASD-AISC provisions. Also, the displacement restrictions are considered in design procedure. The metaheuristic algorithms are encoded in MATLAB interacting with SAP2000 for gathering structural reactions through open application programming interface (OAPI). The optimum spatial steel dome designs achieved by proposed WS, GW, and BSO algorithms are compared with respect to solution accuracy, convergence rates, and reliability, utilizing three real-size design examples for considering both the previously reported optimum design results obtained by classical metaheuristic algorithms and a gradient descent-based hyperband optimization (HBO) algorithm.     

Development of novel processable electron accepting conjugated polymers containing fluoranthene units in the main chain

Considerable interest exists in the development of novel n-type conjugated polymers, since many currently available polymer systems have insufficient electron mobility and/or electron affinity. In this work, a universal synthesis route is presented towards a new class of n-type conjugated polymers, i.e. poly(p-fluoranthene vinylene) (PFV) and its derivatives. This route is illustrated with three examples, i.e. unsubstituted PFV and functionalized hexyl-PFV and dodecyl-PFV. All polymers have been synthesized via the dithiocarbamate precursor route. Solubility was introduced by incorporation of alkyl side chains, which leads to a significantly enhanced purity and processability as compared to unsubstituted PFV. Under the applied electrochemical conditions PFV-type polymers demonstrate typical n-type behavior. Additional CELIV mobility measurements on dodecyl-PFV reveal an excellent electron mobility, μ_e = 1.4 × 10⁻⁴ cm²/Vs. Hence, poly(p-fluoranthene vinylene) and its derivatives are promising n-type materials for organic optoelectronic applications.     

Comparison of eluted monomer from different indirect and direct resin composites

Indirect resin composites used in indirect restorations have been used as alternative methods to avoid the negative effects of a direct application. The composition and structure of these are similar to a direct composite. Several authors have discussed the elution monomer from resin composites because it is a crucial factor in optimizing the physical properties and biocompatibility of resin composites. The aim of this study was to compare the elution of monomers from different resin composites using high-performance liquid chromatography (HPLC). Indirect composites including Signum, Gradia, and Solidex, and direct composite Filtek Ultimate were used. The samples (2 x 5 mm) were prepared and polymerized for 20 seconds with a light-emitting diode unit. A secondary curing was then applied to the indirect resin composites. After fabrication, each sample was immediately immersed in a 75 wt% ethanol/water solution and analyzed by HPLC. The obtained data were analyzed with one-way ANOVA and Tukey HSD (p < 0.05). Residual monomers were eluted from indirect and direct resin composites and the amount of eluted monomers increased over time. The highest mean concentrations of residual Bis-GMA, UDMA, TEGDMA, and HEMA were detected with the Filtek Ultimate (2,342 µM), Solidex (7,908 µM), Signum (2.8 µM), and Filtek Ultimate (9.7 µM), respectively. The highest amount of eluted monomer concentrations detected was viewed as critical for toxic reactions in human cells.     

A new implementation of common matrix approach using third-order tensors for face recognition

In the classical common matrix approach (CMA), the common matrix for each individual face class is obtained using basis matrices calculated by Gram–Schmidt orthogonalization of the class covariance matrix. This common matrix represents the common or invariant properties of a given face class. The CMA idea relies on the concept of basis matrices of a face class which span the, so called, difference subspace of that class. In this paper, an alternative method to obtain the basis matrices for CMA is proposed. The basis matrices are obtained using the higher order singular value decomposition (HOSVD) of a third-order tensor constructed with face images and these basis matrices are utilized in the construction of CMA. In order to exemplify the improvements in the recognition rates, face recognition experiments are carried out via the AR face database. The original face matrices, as well as 2DPCA-, 2DSVD-, and 2DFDA-based feature matrices are applied as the input matrices for the two different implementations of CMA in the experimental studies. The results indicate that the recognition rates obtained by the proposed method are slightly higher than those obtained using the basis matrices calculated by Gram–Schmidt orthogonalization.     

Mechanical properties of reactive powder concrete containing mineral admixtures under different curing regimes

Mechanical properties (compressive strength, flexural strength, and toughness) of reactive powder concrete (RPC) produced with class-C fly ash (FA) and ground granulated blast furnace slag (GGBFS) were investigated under different curing conditions (standard, autoclave and steam curing) in this study. Test results indicate that, compressive strength of RPC increased considerably after steam and autoclaving compared to the standard curing. On the other hand, it was observed that steam and autoclave curing decreased the flexural strength and toughness. Increasing the GGBFS and/or FA content improved the toughness of RPC under all curing regimes considerably. Furthermore, SEM micrographs revealed dense microstructure of RPC.     

Effect of ethanol–gasoline blends on engine performance and exhaust emissions in different compression ratios

Renewable energy sources for the gasoline engines alcohols gain importance recently. These renewable energy sources have attracted the attention of researchers as alternative fuel due to their high octane number. In addition, these are also clean energy sources and can be obtained from the biomass alcohols with low carbon like ethanol. In this study, the effect of compression ratio on engine performance and exhaust emissions was examined at stoichiometric air/fuel ratio, full load and minimum advanced timing for the best torque MBT in a single cylinder, four stroke, with variable compression ratio and spark ignition engine.     

Performance improvement of absorption heat transformer

In this study, a mathematical model of absorption heat transformer (AHT) operating with the aqua/ammonia was developed to simulate the performance of these systems coupled to a solar pond in order to increase the temperature of the useful heat produced by solar ponds and used a special ejector located at the absorber inlet. By the use of the ejector, the obtained absorber pressure becomes higher than the evaporator pressure and thus the system works with triple-pressure-level. The ejector has two functions: (i) aids pressure recovery from the evaporator and (ii) upgrades the mixing process and the pre-absorption by the weak solution of the ammonia coming from the evaporator. The other advantage of the system with ejector is increased absorber temperature. Therefore, pressure recovery and pre-absorption in the ejector improves the efficiency of the AHT. Under the same circumstances, when compared to an AHT with and without an ejector, the system's COP and exergetic coefficient of performance (ECOP) were improved by 14% and 30%, respectively and the circulation ratio (f) was reduced by 57% at the maximum efficiency condition. Due to the reduced circulation ratio, the system dimensions can be reduced; consequently, this decreases overall cost. The maximum upgrading of the solar pond's temperature by the AHT was obtained at 57.5 °C and gross temperature lift at 97.5 °C with coefficients of performance of about 0.5. The maximum temperature of the useful heat produced by the AHT was 150 °C. In addition, exergy losses for each component in the system were calculated at different working temperatures and the results of both systems with and without an ejector were compared. Exergy analysis emphasised that both the losses and irreversibilities have an impact on the system performance and exergy analysis can be used to identify the less efficient components of the system. Exergy analyses also showed that the exergy loss of the absorber of AHT with ejector was higher than those of other components.