Analysis of surface and interior degradation of gas diffusion layer with accelerated stress tests for polymer electrolyte membrane fuel cell

The effects of surface and interior degradation of the gas diffusion layer (GDL) on the performance and durability of polymer electrolyte membrane fuel cells (PEMFCs) have been investigated using three freeze-thaw accelerated stress tests (ASTs). Three ASTs (ex-situ, in-situ, and new methods) are designed from freezing ?30 °C to thawing 80 °C by immersing, supplying, and bubbling, respectively. The ex-situ method is designed for surface degradation of the GDL. Change of surface morphology from hydrophobic to hydrophilic by surface degradation of GDL causes low capillary pressure which decreased PEMFC performance. The in-situ method is designed for the interior degradation of the GDL. A decrease in the ratio of the porosity to tortuosity by interior degradation of the GDL deteriorates PEMFC performance. Moreover, the new method showed combined effects for both surface and interior degradation of the GDL. It was identified that the main factor that deteriorated the fuel cell performance was the increase in mass transport resistance by interior degradation of GDL. In conclusion, this study aims to investigate the causes of degraded GDL on the PEMFC performance into the surface and interior degradation and provide the design guideline of high-durability GDL for the PEMFC.     

Optimization of PEMFC system operating conditions based on neural network and PSO to achieve the best system performance

PEMFC system is a complex new clean power system. Based on MATLAB/Simulink, this paper develops a system-level dynamic model of PEMFC, including the gas supply system, hydrogen supply system, hydrothermal management system, and electric stack. The neural network fits the electric stack model to the simulation data. The effects of different operating conditions on the PEMFC stack power and system efficiency are analyzed. Combining the power of the reactor and the system efficiency to define the integrated performance index, the particle swarm optimization (PSO) algorithm is introduced to optimize the power density and system efficiency of the PEMFC with multiple objectives. The final optimal operating point increases the power density and system efficiency by 1.33% and 12.8%, respectively, which maximizes the output performance and reduces the parasitic power.     

An active balancer with rapid bidirectional charge shuttling and adaptive equalization current control for lithium-ion battery strings

This article proposes an active balancer, which features bidirectional charge shuttling and adaptive equalization current control, to fast counterbalance the state of charge (SOC) of cells in a lithium-ion battery (LIB) string. The power circuit consists of certain bidirectional buck-boost converters to transfer energy among the different cells back and forth. Owing to the characterization of the open-circuit voltage (OCV) vs SOC in LIB being relatively smooth near the SOC middle range, the SOC-inspected balance strategy can achieve more precise and efficient equilibrium than the voltage-based control. Accordingly, a compensated OCV-based SOC estimation is put forward to take into account the discrepancy of SOC estimation. Besides, the varied-duty-cycle (VDC) and curve-fitting modulation (CFM) methods are devised herein to tackle the problems of slow equalization rate and low balance efficacy, which arise from the diminution in balancing current as the SOC difference between the cells decreases in the later duration of equalization especially. The proposed strategies have taken the battery nonlinear characteristic and circuit parameter nonideality into account and can adaptively modulate the duty cycle with the SOC difference to keep balancing current constant throughout the balancing cycle. Simulated and experimental results are given to demonstrate the feasibility and effectiveness of the same prototype constructed. Compared with the fixed duty cycle and the VDC methods, the proposed CFM has the best balancing efficiency of 81.4%, and the balance time is shortened by 27.1% and 18.6%, respectively.     

Rheological and viscoelastic properties of colloidal solutions based on gelatins and chitosan as affected by pH

The objective of this study was to evaluate the influence of pH on rheological and viscoelastic properties of solutions based on blends of type A (GeA) or type B (GeB) gelatin and chitosan (CH). Solutions of GeA, GeB, CH, GeA:CH, and GeB:CH were prepared in several pH (3.5–6.0) and analyzed for determination of zeta-potential. Rheological analyses (stationary and dynamic essays) were carried out with blends allowing to study the effect of pH on shear stress, apparent viscosity, loss (G”) and storage (G’) moduli, and angle phase (Tanδ). Zeta potential of all biopolymers decreased linearly as a function of pH. CH presented higher values, and GeB, the lowest one, being the only having negative values at pH > 5. Overall, the pH influenced the rheological and viscoelastic properties of the colloidal solutions: shear stress and apparent viscosity increased as a function of pH. Other assays were carried out at 3% and 5% strain, for GeA:CH and GeB:CH, respectively. In the sol domain, G’ and G” (1 Hz) increased linearly for GeA:CH. But for GeB:CH, they increased in two linear different regions: one function between pH 3.5 and 5.0 and another one between 5.0 and 6.0, being a more important effect was visible in this last domain probably due to the negative net charge of gelatin, above it pI. An effect in two domains was also visible for Tanδ, explained in the same manner as previously. The GeB:CH blends behaved like diluted solutions, and transition temperatures increased as a function of pH.     

Physical and sensory properties of lemon-flavored acidic beverages formulated with nonfat dry milk during storage

Sensory and physical properties of 2 lemon-flavored beverages with 5% and 7.5% wt/wt nonfat dry milk (NFDM) at pH 2.5 were studied during storage. The 2 beverages had similar volatile compounds, but the 5% NFDM had higher aroma and lemon flavor, with a preferred appearance by consumers due to the lower turbidity and viscosity. After 28 d of storage at 4°C, lemon flavor decreased in the 5% NFDM beverage but was still more intense than the 7.5% one. During 70 d of storage, no microorganisms were detected, and the beverages were more stable when stored at 4°C than at room temperature according to changes of physical properties measured for appearance, turbidity, color, particle size, zeta potential, rheological properties, and transmission electron microscopy morphology. Findings of the present study suggest that NFDM may be used at 5% wt/wt to produce stable acidic dairy beverages with low turbidity when stored at 4°C.     

Gluten–starch interface characteristics and wheat dough rheology—Insights from hybrid artificial systems

Referring to the total surface existing in wheat dough, gluten–starch interfaces are a major component. However, their impact on dough rheology is largely unclear. Common viewpoints, based on starch surface modifications or reconstitution experiments, failed to show unambiguous relations of interface characteristics and dough rheology. Observing hybrid artificial dough systems with defined particle surface functionalization gives a new perspective. Since surface functionalization standardizes particle–polymer interfaces, the impact on rheology becomes clearly transferable and thus, contributes to a better understanding of gluten–starch interfaces. Based on this perspective, the effect of particle/starch surface functionality is discussed in relation to the rheological properties of natural wheat dough and modified gluten–starch systems. A competitive relation of starch and gluten for intermolecular interactions with the network-forming polymer becomes apparent during network development by adsorption phenomena. This gluten–starch adhesiveness delays the beginning of non-linearity under large deformations, thus contributing to a high deformability of dough. Consequently, starch surface functionality affects the mechanical properties, starting from network formation and ending with the thermal fixation of structure.     

南方地区造纸车间钢屋面保温厚度的计算与分析

本文从内表面防结露、夏季隔热2个角度出发，对夏热冬冷及夏热冬暖地区代表城市采用的钢结构屋面的保温（隔热）层厚度进行计算分析。研究表明，在夏季室内温、湿度达到某一状态时，隔热厚度要大于冬季防结露的保温厚度。因此，夏热冬冷地区的造纸车间钢屋面保温层厚度应按夏季隔热计算确定，并进行冬季防结露验算；夏热冬暖地区按照冬季防结露计算即可。     

Vertex-Edge Degree Based Indices of Honey Comb Derived Network

Chemical graph theory is a branch of mathematics which combines graph theory and chemistry. Chemical reaction network theory is a territory of applied mathematics that endeavors to display the conduct of genuine compound frameworks. It pulled the research community due to its applications in theoretical and organic chemistry since 1960. Additionally, it also increases the interest the mathematicians due to the interesting mathematical structures and problems are involved. The structure of an interconnection network can be represented by a graph. In the network, vertices represent the processor nodes and edges represent the links between the processor nodes. Graph invariants play a vital feature in graph theory and distinguish the structural properties of graphs and networks. In this paper, we determined the newly introduced topological indices namely, first -degree Zagreb index, first -degree Zagreb index, second -degree Zagreb index, -degree Randic index, -degree atom-bond connectivity index, -degree geometric-arithmetic index, -degree harmonic index and -degree sum-connectivity index for honey comb derived network. In the analysis of the quantitative structure property relationships (QSPRs) and the quantitative structureactivity relationships (QSARs), graph invariants are important tools to approximate and predicate the properties of the biological and chemical compounds. Also, we give the numerical and graphical representation of our outcomes.     

Mechanism for the hydrolysis resistance of aluminum nitride powder modified by boric acid

Aluminum nitride (AlN) ceramics are becoming cutting-edge materials for electronic information and communication. However, raw AlN hydrolyzed rapidly, and the high storage costs of this material prevent widespread application. In this study, raw AlN was modified by boric acid (H₃BO₃) at 30 °C to enhance hydrolysis resistance. Transmission electron microscope (TEM), X-ray diffraction (XRD), the magic angle spinning nuclear magnetic resonance (²⁷Al-MAS-NMR and ¹¹B-MAS-NMR), and the fourier transform infrared spectrometer (FTIR) were used to characterize the powder before and after treatment, and the mechanism of hydrolysis resistance was determined. Modification with 0.1 M boric acid did not change the crystal phase of the AlN particles. The modified powder did not hydrolyse at 90% humidity and 70° Celsius. In the presence of boric acid, a network structure of B–O–B linkages ([BO_n], n = 3 or 4) formed that was connected to the AlN core via chemical bonds of B–N–Al and B–O–Al. The protective 6 – 10 nm-thick layer that formed on the surface of the AlN crystal, prevented attack by water molecules and hindered the hydrolysis of aluminium nitride. This study provides an alternative means of preparing anti-hydrolysis AlN powders.