Physical quality and in vitro starch digestibility of bread as affected by addition of extracted malva nut gum

Malva nut gum (MNG) was extracted by alkaline solution. The previous studies showed that the extract had viscosity and gelling properties as well as inhibited α-amylase activity in starch solution 1.5–2.0 folds higher than that of original malva nut gum. This research was aimed to investigate the α-amylase inhibitory effect of alkaline-extracted MNG in solid food and to determine physical properties of MNG-containing bread. The scanning electron microscopy of in vitro digestibility with α-amylase of MNG-containing breads showed less porosity and more undigested starch granules remained intact with the matrix compared to control. This finding was consistent with the reduction of glucose (33–40%) and maltose (23–39%) levels compared to that of control after α-amylase digestion for 180 min in a dialysis system. The results showed that extracted MNG significantly (p < 0.05) increased loaf volume, and moisture content by 1.5–12%, and 8.2–12.8%, respectively compared to that of control. Addition of extracted MNG in bread formulation significantly reduced moisture loss and firmness of the bread crumb after storage for three days.     

Influence of Specimen Layout on 17-4PH (AISI 630) Alloys Fabricated by Low-Cost Additive Manufacturing

This work examined the effects of specimen layout on physical, microstructural, and mechanical properties of 17-4PH (AISI 630) fabricated by metal-fused deposition modeling process. Tensile specimens were 3D-printed with the different layouts using 100 pct infill. The as-printed and as-sintered specimens with the flat layout had the best appearance, green, relative sintered density, and sintered tensile properties with good repeatability, while the specimens with the vertical layout were the worst. The as-sintered tensile properties of specimens with the side layout were slightly lower than those with the flat layout but significantly higher than those with the vertical layout. Moreover, the tensile properties of specimens with the flat and side layouts met the Metal Powder Industry Federation standard 35 for metal injection molding. The tensile properties and corresponding fracture surfaces can be explained in terms of the combined effect of load-bearing and stress concentration due to the pre-existence of voids at perimeters. The fracture surfaces of specimens with the vertical layout showed large defects induced during printing and voids between perimeter walls generating high stress concentration and layer delamination. The difference between tensile properties of specimens with the side and flat layouts is mainly due to the characteristic of the printing—voids in the side layout are larger and more detrimental to the mechanical properties—which was confirmed by the evidence of cracking in the fracture surface.

     

In vitro retardation of glucose diffusion with gum extracted from malva nut seeds produced in Thailand

Mucilage of malva nut fruit has been used as traditional medicine in Thailand. Our laboratory has succeeded in extracting malva nut gum (MNG) from malva nut seeds by using alkaline-extraction method. The extract had higher gelling properties compared to water-extracted MNG. This research was aimed to investigate the effect of MNG on the retardation of glucose diffusion in in vitro dialysis processes. The results showed that alkaline-extracted MNG significantly (p < 0.05) reduced glucose content in dialysate compared to control containing no dietary fibre. MNG at 1% (w/w) concentration was more effective than that of 0.5% (w/w) concentration. The mixture of MNG and guar gum significantly (p < 0.05) reduced glucose in dialysate by 50–82% compared to that of control. In starch digestion process, the mixture of MNG and guar gum showed greater reduction of glucose (3–7 folds) in dialysate at 15–30 min.     

Mechanical Properties Amelioration of Hybrid Composites by Concomitant Synergy Between Graphene Oxide and Silica Nanoparticles

氧化石墨烯和二氧化硅纳米颗粒协同作用下的

复合材料力学性能改善

Anchalee Duongthipthewa, 杨树明*,王一鸣

（西安交通大学 机械制造系统工程国家重点实验室,西安 710049）

创新点说明：

本文提出将氧化石墨烯和纳米二氧化硅颗粒组成的纳米复合材料作为填充物添加到环氧树脂/碳纤维复合材料体系中,用于提升其机械性能和湿润环境下的抗腐蚀性。

研究目的：

通过实验研究了氧化石墨烯和纳米二氧化硅颗粒组成的纳米复合材料作为填充物对环氧树脂/碳纤维复合材料体系的机械性能增强作用,以及在湿润环境下的抗腐蚀性。

研究方法：

本文通过真空辅助树脂传递模塑（VARTM）方法制备了环氧树脂/碳纤维复合材料样品,同时也通过该方法向复合材料体系中添加了不同分量的氧化石墨烯和纳米二氧化硅颗粒组成的纳米复合填料;通过三点弯曲测试、冲击实验、硬度测试和动态力学分析等方法对所制备样品的弯曲强度、冲击强度、硬度等机械性能进行了测量;通过分别在纯水和盐水中浸泡2周,对样品的吸湿性、烘干后的重量保留和性能保留进行了分析测试。

结果：

实验结果表明,对于添加了氧化石墨烯和纳米二氧化硅颗粒组成的纳米复合材料作为填充物的环氧树脂/碳纤维复合材料体系,其机械性能表现出全面的明显提升,包括弯曲强度、冲击强度、硬度等;纳米二氧化硅分量的提高还会使其性能得到进一步提升;对于含有复合纳米填充物的样品,其暴露在湿润环境中时虽然吸湿度较高,但烘干后重量损失反而较小,而且再次对其机械性能进行测试后发现其性能保留程度也较高;同样的,含有高分量纳米二氧化硅的样品性能表现最优。为探究其增强原理,通过扫描电子显微镜对样品断面进行了分析。

结论：

实验结果显示,复合填充物的存在使整个复合材料体系的机械强度得到提升,其根本原因在于复合填充材料的存在使环氧树脂与碳纤维骨架的结合更加紧密,在收到外力作用时应力得以迅速传递避免累积,扫描电子显微镜的结果也支持该结论。

关键词：复合材料,纳米填充,机械性能,热分析,吸湿性

     

Effects of humidity and contact material on fretting fatigue behavior of an extruded AZ61 magnesium alloy

Fretting fatigue tests of the extruded AZ61 magnesium alloy with the same contact material under low and high humidity were carried out to investigate basic fretting fatigue characteristics and effect of humidity on fretting fatigue behavior. Influence of contact material was also studied by using JIS S45C carbon steel contact material. Degradation of fatigue strength due to fretting was much more significant than that due to corrosion under high humidity condition. Therefore, no effect of humidity on fretting fatigue strength was found. Reduction rate of fatigue strength due to fretting for the magnesium alloy was between those of aluminum alloys and titanium alloys. Tangential force coefficient of the magnesium alloy was rather low compared to other materials such as steels, aluminum alloys and titanium alloys. Fretting fatigue strength with the S45C contact material was inferior compared to that with the same contact material. This is mainly due to higher tangential force in AZ61/S45C contact. Fretting fatigue cracks at the edge of fretting contact region were observed to nucleate in the very early stage of fatigue life, similar to other structural materials.     

Classification of linear and non-linear modulations using the Baum–Welch algorithm and MCMC methods

Satellite transmissions classically use constant amplitude linear modulation schemes, such as M-state phase shift keying (M-PSK), because of their high robustness to amplifier non-linearities. However, other modulation formats are interesting in a satellite transmission context. For instance, non-linear modulations such as Gaussian minimum shift keying (GMSK) present a higher spectral efficiency and appear in new standards for telemetry/telecommand satellite links. Another example is offset-QPSK (OQPSK) modulation that allows one to decrease the out-of-band interference due to band limiting and the non-linearity of the amplifier. To get a compromise between the robustness to amplifier non-linearities provided by MPSK modulation and the spectral efficiency given by QAM modulation, the recent broadcasting satellite standard (DVB-S2) proposes new modulation schemes called APSK. Obviously, all satellite systems that use various modulation schemes will have to co-exist. In this context, modulation recognition using the received communication signal is essential. In that context, this paper studies two Bayesian classifiers to recognize linear and non-linear modulations. These classifiers estimate the posterior probabilities of the received signal, given each possible modulation, and plug them into the optimal Bayes decision rule. Two algorithms are used for that purpose. The first one generates samples distributed according to the posterior distributions of the possible modulations using Markov chain Monte Carlo (MCMC) methods. The second algorithm estimates the posterior distribution of the possible modulations using the Baum–Welch (BW) algorithm. The performance of the resulting classifiers is assessed through several simulation results.     

Rheological properties of extracted malva nut gum (Scaphium scaphigerum) in different conditions of solvent

Mucilage of malva nut fruit has been used as traditional medicine in Thailand. Health benefits of this mucilage are linked to its gelling property. This research was aimed to evaluate oscillatory rheological properties of malva nut gum (MNG) in different conditions of solvent (pH, ionic strength, and co-solutes addition). A small strain oscillation (0.1% strain) was used to investigate gelling properties of MNGs extracted with alkaline solutions compared to original MNG. Alkaline extracted MNGs showed higher storage modulus than did the original MNG. FT-IR of alkaline extracted MNGs showed carboxylic bonds with the reduction of galacturonic acids to increase the storage modulus compared to that of original MNG. Sodium chloride and calcium chloride strongly influenced the swelling of MNG, while the effect was smaller with K⁺ and Mg²⁺ ions. Addition of 5% sucrose into MNG solution increased gel strength of the polymer more than that of MNG solution containing 10% sucrose. Addition of guar gum into MNG solution increased storage modulus in either salts or acid containing system.