Acoustic Properties of Aerogels: Current Status and Prospects

Noise reduction remains an important priority in the modern society, in particular, for urban areas and highly populated cities. Insulation of buildings and transport systems such as cars, trains, and airplanes has accelerated the need to develop advanced materials. Various porous materials, such as commercially available foams and granular and fibrous materials, are commonly used for sound mitigating applications. In this review, a special class of advanced porous materials, aerogels, is examined, and an overview of the current experimental and theoretical status of their acoustic properties is provided. Aerogels can be composed of inorganic matter, synthetic or natural polymers, as well as organic/inorganic composites and hybrids. Aerogels are highly porous nanostructured materials with a large number of meso- and small macropores; the mechanisms of sound absorption partly differ from those of traditional porous absorbers possessing large macropores. The understanding of the acoustic properties of aerogels is far from being complete, and experimental results remain scattered. It is demonstrated that the structure of the aerogel provides a complex three-dimensional architecture ideally suited for promising high-performance materials for acoustic mitigation systems. This is in addition to the numerous other desirable properties that include low density, low thermal conductivity, and low refractive index.     

Compressional wave velocity of hydrate-bearing bentheimer sediments with varying pore fillings

A potential alternative energy resource to meet energy demands is the vast amount of gas stored in hydrate reserves. However, major challenges in terms of exploration and production surround profitable and effective exploitation of these reserves. The measurement of acoustic velocity is a useful method for exploration of gas hydrate reserves and can be an efficient method to characterize the hydrate-bearing sediments. In this study, the compressional wave velocity (P-wave velocity) of consolidated sediments (Bentheimer) with and without tetrahydrofuran hydrate-bearing pore fillings were measured using the pulse transmission method. The study has found that the P-wave velocity of consolidated sediments increase with increasing hydrate formation and confining pressure. Of the two samples tested, the increase in wave velocity of the dry and hydrate-bearing samples amounted to 27.6% and 31.9%, respectively. Interestingly, at the initial stage of hydrate formation, there was no change in P-wave velocity, which was followed by a steady increase as the hydrate crystals began to agglomerate and then it increased rapidly to a constant value, suggesting that the test solution had converted to a hydrate solid.     

An efficient statistical zero-knowledge authentication protocol for smart cards

We construct an efficient statistical zero-knowledge authentication protocol for smart cards based on general assumptions. We show how it can be instantiated using lattice-based primitives, which are conjectured to be secure against quantum attacks. We illustrate the practicality of our protocol on smart cards in terms of storage, computation, communication, and round complexities. Furthermore, we compare it to other lattice-based authentication protocols, which are either zero-knowledge or have a similar structure. The comparison shows that our protocol improves the best previous protocol in several aspects.     

Prebiotics as functional foods: A review

Prebiotics are short chain carbohydrates that are non-digestible by digestive enzymes in humans and selectively enhance the activity of some groups of beneficial bacteria. In the intestine, prebiotics are fermented by beneficial bacteria to produce short chain fatty acids. Prebiotics also render many other health benefits in the large intestine such as reduction of cancer risk and increase calcium and magnesium absorption. Prebiotics are found in several vegetables and fruits and are considered functional food components which present significant technological advantages. Their addition improves sensory characteristics such as taste and texture, and enhances the stability of foams, emulsions and mouthfeel in a large range of food applications like dairy products and bread. This contribution reviews bioactives from food sources with prebiotic properties. Additionally, food application of bioactive prebiotics, stimulation of the viability of probiotics, health benefits, epidemiological studies, and safety concerns of prebiotics are also reviewed.     

Seawater Pretreatment by Microfiltration: An Economic Assessment

This paper conducts cost and economic analyses of the microfiltration system (MFS) seawater pretreatment technique for reverse osmosis (RO) application. The study is based on operational results from an RO plant in Kuwait and, for the sake of comparability, the analysis follows the same approach as the earlier studies that evaluated the cost-effectiveness of alternative techniques. The analysis shows that the MFS is as cost-effective as the beachwell system, which gives substantial cost savings compared with the conventional surface system.     

Hydrogen production from methane dry reforming over nickel-based nanocatalysts using surfactant-assisted or polyol method

In this study, two series of Ni-based nanocatalysts were synthesized successfully by the polyol and surfactant-assisted methods and subsequently tested for hydrogen production from CO₂–CH₄ reforming. Surfactant-assisted catalysts were prepared by using cetyl trimethyl ammonium bromide (CTAB) as a surfactant, whereas polyol catalysts were prepared in ethylene glycol (EG) medium with polyvinylpyrrolidone (PVP) as a nucleation-protective agent. The catalytic performance of each catalyst, in terms of H₂ yield and selectivity, was evaluated at different temperatures (500–800 °C). In order to clarify and explain the differences in catalytic activities of catalysts, the prepared samples were characterized by various techniques, such as BET, H₂-TPR, CO₂-TPD, XRD, TGA, SEM, HRTEM and CO pulse chemisorption. The results demonstrated that the method of preparation had a significant effect on the catalytic performance of tested catalysts. Overall, polyol catalysts showed high activity and selectivity for hydrogen production, while surfactant-assisted catalysts exhibited a fairly high resistance towards carbon deposition under similar reaction conditions of dry reforming of methane. Moreover, due to the reverse water gas shift reaction (RWGS), surfactant-assisted catalysts always produced smaller values of H₂/CO product ratio than their corresponding polyol catalysts.     

Viability and Activity of Bifidobacteria During Refrigerated Storage of Yoghurt Containing Mangifera pajang Fibrous Polysaccharides

Abstract: The viability and activity of Bifidobacterium pseudocatenulatum G4, B. longum BB 536 and yoghurt cultures (Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus) were studied in yoghurt containing 0.75%Mangefira pajang fibrous polysaccharides (MPFP) and inulin. Growth of probiotic organisms, their proteolytic activities, the production of short chain fatty acids (lactic, acetic and propionic) and the pH of the yoghurt samples were determined during refrigerated storage at 4 °C for 28 d. B. pseudocatenulatum G4 and B. longum BB 536 showed better growth and activity in the presence of MPFP and inulin, which significantly increased the production of short chain fatty acids as well as the proteolytic activity of these organisms. Practical Application: This is the first study reported on produce synbiotic yoghurt as a functional food for specified health uses contains bifidobacteria and M. pajang fibrous polysaccharides. M. pajang fibrous polysaccharides can be used as a prebiotic particularly in dairy products to increase the viability and activity of bifidobacteria which can be used as probiotic to exert health benefit to the human by yoghurt that is considered common use in society; thus, the benefits of synbiotic yoghurt are readily accessible to the member of society.     

Ni supported on La2O3+ZrO2 for dry reforming of methane: The impact of surface adsorbed oxygen species

This research investigates the effect of doping Ni/La₂O₃+ZrO₂ with nitrates of Ca, Cr, Ga, and Gd on the conversion of the feed and H₂/CO molar ratio. The development of these catalysts is intended to tackle inefficiency of dry reforming of CH₄ which stems from deactivation and sintering of active metal. All promoted catalysts perform better than the un-promoted catalyst. Cr promoted sample gives the best performance with CH₄ and CO₂ conversion averaging 83 and 88% respectively. Also, it maintains good stability. The relative ease of reducing the catalyst plus its porous nature are responsible for its performance. Ca promoted sample has the same area as that of the support indicating the movement of Ni–Ca out of the pores of the support during calcination. According to thermogravimetric analysis, the un-promoted catalyst records the highest amount of carbon while the Ca promoted sample has about 18%.