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Topic Review
Steady State
In chemistry, a steady state is a situation in which all state variables are constant in spite of ongoing processes that strive to change them. For an entire system to be at steady state, i.e. for all state variables of a system to be constant, there must be a flow through the system (compare mass balance). A simple example of such a system is the case of a bathtub with the tap running but with the drain unplugged: after a certain time, the water flows in and out at the same rate, so the water level (the state variable Volume) stabilizes and the system is in a steady state. The steady state concept is different from chemical equilibrium. Although both may create a situation where a concentration does not change, in a system at chemical equilibrium, the net reaction rate is zero (products transform into reactants at the same rate as reactants transform into products), while no such limitation exists in the steady state concept. Indeed, there does not have to be a reaction at all for a steady state to develop. The term steady state is also used to describe a situation where some, but not all, of the state variables of a system are constant. For such a steady state to develop, the system does not have to be a flow system. Therefore, such a steady state can develop in a closed system where a series of chemical reactions take place. Literature in chemical kinetics usually refers to this case, calling it steady state approximation. In simple systems the steady state is approached by state variables gradually decreasing or increasing until they reach their steady state value. In more complex systems state variable might fluctuate around the theoretical steady state either forever (a limit cycle) or gradually coming closer and closer. It theoretically takes an infinite time to reach steady state, just as it takes an infinite time to reach chemical equilibrium. Both concepts are, however, frequently used approximations because of the substantial mathematical simplifications these concepts offer. Whether or not these concepts can be used depends on the error the underlying assumptions introduce. So, even though a steady state, from a theoretical point of view, requires constant drivers (e.g. constant inflow rate and constant concentrations in the inflow), the error introduced by assuming steady state for a system with non-constant drivers may be negligible if the steady state is approached fast enough (relatively speaking).
  • 1.0K
  • 14 Oct 2022
Topic Review
Status of Health Estimation Methods
As the backup power supply of power plants and substations, Valve Regulated Lead Acid (VRLA) batteries are the last safety guarantee for the safe and reliable operation of power systems, and the batteries status of health（SOH）directly affects the stability and safety of power system equipment. In recent years, due to the aging and failure of VRLA batteries, some serious safety accidents have been caused, so it is very necessary to accurately evaluate the health of batteries.
  • 676
  • 21 Mar 2023
Topic Review
Starch–Mucilage Composite Films
Generally, starch is an edible carbohydrate complex, composed of a linear polymer, amylose (a linear molecule with few branches), and amylopectin (branched-chain molecule). Therefore, the presence of amylose in large quantities provides excellent strength while a high level of amylopectin is responsible for the reduction of the tensile strength during the production of a film. However, starch-based films have limitations in their ability to bear various environmental factors such as temperature, pressure, and natural gases during the handling due to their low strength, flexibility, rigidity, and high hydrophilic nature. To overcome this issue, the combination of starch and mucilage can be used as a binary polymer alternative to improve the mechanical properties of the packaging film. Additionally, the addition of several biopolymers such as cellulose, gum, and gelatin into a starch blend can change the network formation in the film matrix, improving the physicochemical and biological properties of the film. Moreover, mucilage is a water-soluble edible polysaccharide, extensively used in the food industry due to its excellent functional properties (antimicrobial, antioxidant, water-holding, oil holding, and foaming capacity), and diverse industrial applications such as thickening agent, binding agent, emulsifying agent, and suspending agent. Mucilage has a great potential to produce a stable polymeric network that confines the starch granules, which delay the release of amylose in resulting the improvement of the mechanical property of films.
  • 1.7K
  • 17 Aug 2021
Topic Review
Starch-Based Materials for Food Packaging
The food packaging sector generates large volumes of plastic waste due to the high demand for packaged products with a short shelf-life. Biopolymers such as starch-based materials are a promising alternative to non-renewable resins, offering a sustainable and environmentally friendly food packaging alternative for single-use products. 
  • 1.2K
  • 25 Jan 2022
Topic Review
Starch-Based Materials
Starch is one of the most common biodegradable polymers found in nature, and it is widely utilized in the food and beverage, bioplastic industry, paper industry, textile, and biofuel industries. Starch has received significant attention due to its environmental benignity, easy fabrication, relative abundance, non-toxicity, and biodegradability. 
  • 1.4K
  • 25 Nov 2021
Topic Review
Starch-Based Biodegradable Films for Food Packaging
The use of biodegradable packaging material as an alternative to conventional petrochemical-based polymers is based on the environmental issues associated with conventional materials. Starch-based biodegradable films can be applied in food packaging. It was evident that starch stands out among biopolymers due to its abundance and cost effectiveness.
  • 3.0K
  • 07 Apr 2022
Topic Review
Standards on Occupational Risk and Safety of Nanotechnology
Nanomaterials offer new technical and commercial opportunities but, due to their low particle size, raise occupational health and safety concerns and may also pose risks to the consumers and the environment. Many standards at the ISO level, or at European level, have been developed in the area of nanotechnologies, taking into account, namely, occupational risk and safety. 
  • 623
  • 14 Mar 2022
Topic Review
Stacking
In chemistry, pi stacking (also called π–π stacking) refers to attractive, noncovalent interactions between aromatic rings, since they contain pi bonds. These interactions are important in nucleobase stacking within DNA and RNA molecules, protein folding, template-directed synthesis, materials science, and molecular recognition, although new research suggests that pi stacking may not be operative in some of these applications. Despite intense experimental and theoretical interest, there is no unified description of the factors that contribute to pi stacking interactions.
  • 708
  • 31 Oct 2022
Topic Review
Stabilization of Hexa-Histidine-Containing Organophosphorus Hydrolase
Organophosphorus hydrolase, containing a genetically introduced hexahistidine sequence (His6-OPH) can hydrolyze various  substrates, such as  organophosphorus pesticides and chemical warfare agents, mycotoxins, and N-acyl homoserine lactones. The application of various carrier materials (metal-organic frameworks, polypeptides, bacterial cellulose, polyhydroxybutyrate, succinylated gelatin, etc.) for the immobilization and stabilization of His6-OPH by various methods, enables creation of biocatalysts with various properties and potential uses, in particular, as antidotes, recognition elements of biosensors, in fibers with chemical and biological protection, dressings with antimicrobial properties, highly porous sorbents for the degradation of toxicants, including in flow systems, etc. Immobilized variants of His6-OPH are characterized by increased stability, and the hydrolytic process of destruction of many substrates can be carried out in wider temperature and pH ranges than when using a free form of the enzyme. The variation in methods and carriers for the immobilization of His6-OPH makes it possible to create a wide palette of biocatalysts, significantly expanding the boundaries of enzyme use.
  • 343
  • 14 Feb 2023
Topic Review
Stability of Cu-Based Catalysts for Methanol Reforming
The stability of copper-based catalysts is an important property that affects the catalytic efficiency, which determines the service life of the catalytic base in the methanol steam reforming (MSR) reaction, and plays an important role in the sustainable production of hydrogen.
  • 774
  • 21 Jul 2022
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