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Topic Review
Sulfate-Reducing Microorganisms
Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate (SO42–) as terminal electron acceptor, reducing it to hydrogen sulfide (H2S). Therefore, these sulfidogenic microorganisms "breathe" sulfate rather than molecular oxygen (O2), which is the terminal electron acceptor reduced to water (H2O) in aerobic respiration. Most sulfate-reducing microorganisms can also reduce some other oxidized inorganic sulfur compounds, such as sulfite (SO32–), dithionite (S2O42–), thiosulfate (S2O32–), trithionate (S3O62–), tetrathionate (S4O62−), elemental sulfur (S8), and polysulfides (Sn2−). Depending on the context, "sulfate-reducing microorganisms" can be used in a broader sense (including all species that can reduce any of these sulfur compounds) or in a narrower sense (including only species that reduce sulfate, and excluding strict thiosulfate and sulfur reducers, for example). Sulfate-reducing microorganisms can be traced back to 3.5 billion years ago and are considered to be among the oldest forms of microbes, having contributed to the sulfur cycle soon after life emerged on Earth. Many organisms reduce small amounts of sulfates in order to synthesize sulfur-containing cell components; this is known as assimilatory sulfate reduction. By contrast, the sulfate-reducing microorganisms considered here reduce sulfate in large amounts to obtain energy and expel the resulting sulfide as waste; this is known as dissimilatory sulfate reduction. They use sulfate as the terminal electron acceptor of their electron transport chain. Most of them are anaerobes; however, there are examples of sulfate-reducing microorganisms that are tolerant of oxygen, and some of them can even perform aerobic respiration. No growth is observed when oxygen is used as the electron acceptor. In addition, there are sulfate-reducing microorganisms that can also reduce other electron acceptors, such as fumarate, nitrate (NO3−), nitrite (NO2−), ferric iron [Fe(III)], and dimethyl sulfoxide. In terms of electron donor, this group contains both organotrophs and lithotrophs. The organotrophs oxidize organic compounds, such as carbohydrates, organic acids (e.g., formate, lactate, acetate, propionate, and butyrate), alcohols (methanol and ethanol), aliphatic hydrocarbons (including methane), and aromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylene). The lithotrophs oxidize molecular hydrogen (H2), for which they compete with methanogens and acetogens in anaerobic conditions. Some sulfate-reducing microorganisms can directly utilize metallic iron [Fe(0)] as electron donor, oxidizing it to ferrous iron [Fe(II)].
  • 6.6K
  • 04 Nov 2022
Topic Review
Hydrothermal Liquefaction of Biomass
Hydrothermal liquefaction is a high-temperature high-pressure thermochemical conversion method adapted to convert high-water content biomass feedstocks to biofuels and many other valuable industrial chemicals. The hydrothermal process is broadly classified into carbonization, liquefaction, and gasification with hydrothermal liquefaction conducted in the intermediate temperature range of 250–374 °C and pressure of 4–25 MPa. Over the years, various solvents and co-solvents have been used as conversion mediums to promote easy decomposition of the lignocellulosic components in biomass. To obtain the final products, the product separation process typically involves multiple extraction and evaporation steps, which greatly depend on the type of extractive solvents and process parameters. In general, the main aim of the hydrothermal process is to produce a primary product, such as bio-oil, biochar, gases, or industrial chemicals, such as adhesives, benzene, toluene, and xylene.
  • 6.6K
  • 19 Aug 2021
Topic Review
Mini-LED and Micro-LED
The mini-LEDs with chip sizes ranging from 100 to 200 μm have already been commercialized for backlight sources in consumer electronics applications. The realized local diming can greatly improve the contrast ratio at relatively low energy consumptions. The micro-LEDs with chip size less than 100 μm, still remain in the laboratory.
  • 6.6K
  • 24 Jun 2021
Topic Review
Cigarette Filter
A cigarette filter is a component of a cigarette, along with cigarette paper, capsules and adhesives. It does not make cigarettes less unhealthy. The filter may be made from cellulose acetate fibre, paper or activated charcoal (either as a cavity filter or embedded into the cellulose acetate). Macroporous phenol-formaldehyde resins and asbestos have also been used in cigarette filters. The acetate and paper modify the particulate smoke phase by particle retention (filtration), and finely divided carbon modifies the gaseous phase (adsorption). Filters can reduce "tar" and nicotine smoke yields up to 50%, with a greater removal rate for other classes of compounds (e.g., phenols), but are ineffective in filtering toxins such as carbon monoxide. Most of these measured reductions occur only when the cigarette is smoked on a smoking machine; when a human smokes them, deliveries remain similar with or without a filter. Most factory-made cigarettes are equipped with a filter; those who roll their own can buy them from a tobacconist. The near-universal adoption of filters on cigarettes has not reduced harms to smokers; for instance, lung cancer rates have not declined. Filling a given length of cigarette with filter is cheaper than filling it with tobacco.
  • 6.6K
  • 10 Nov 2022
Topic Review
Visual Appearance of Oil
The visual appearance of oil spills at sea is often used as an indicator of spilled oil properties, state and slick thickness. These appearances and the oil properties that are associated with them are reviewed in this entry. The appearance of oil spills is an estimator of thickness of thin oil slicks, thinner than a rainbow sheen (<3 µm). Rainbow sheens have a strong physical explanation. Thicker oil slicks (e.g., >3 µm) are not correlated with a given oil appearance. At one time, the appearance of surface discharges from ships was thought to be correlated with discharge rate and vessel speed; however, this approach is now known to be incorrect. Oil on the sea can sometimes form water-in-oil emulsions, dependent on the properties of the oil, and these are often reddish in color. These can be detected visually, providing useful information on the state of the oil. Oil-in-water emulsions can be seen as a coffee-colored cloud below the water surface. Other information gleaned from the oil appearance includes coverage and distribution on the surface.
  • 6.6K
  • 27 Jan 2021
Topic Review
Sesquiterpene Lactones
Sesquiterpene lactones, a vast group of terpenoids isolated from Asteraceae family species, exhibit a wide variety of biological activities and several of them are already available on the medicines market, such as artemisinin. Here are presented and discussed the most recent and impactful results in vivo, preclinical and clinical studies, involving a selection of ten sesquiterpene lactones (alantolactone, arglabin, costunolide, cynaropicrin, helenalin, inuviscolide, lactucin, parthenolide, thapsigargin and tomentosin) and some of their derivatives.
  • 6.6K
  • 28 Oct 2020
Topic Review
Brassicaceae Family
Brassicaceae family vegetables have an ample worldwide distribution, which can be found in all continents except Antarctica. One of the most striking features of this botanical family is the presence of several kinds of secondary metabolites with a distinctive taste, and also interesting bioactivities. The most deeply studied are the glucosinolates (GSL) and from their bioactive breakdown products, the isothiocyanates and the indoles. Moreover, these species are also rich and possess unique profiles of phenolic compounds, carotenoids, and other groups of less studied compounds such as phytoalexins, terpenes, phytosteroids, and tocopherols, here reviewed.
  • 6.6K
  • 29 Oct 2020
Topic Review
Paradigm Shift
A paradigm shift refers to a fundamental change in the underlying assumptions, beliefs, or frameworks that guide a particular field of knowledge or practice. It represents a transformative departure from established models of thought, leading to a reevaluation of existing principles and often opening new avenues for understanding and problem-solving within that domain.
  • 6.6K
  • 25 Jan 2024
Topic Review
Gaia Hypothesis
The Gaia hypothesis (/ˈɡaɪ.ə/), also known as the Gaia theory, Gaia paradigm, or the Gaia principle, proposes that living organisms interact with their inorganic surroundings on Earth to form a synergistic and self-regulating, complex system that helps to maintain and perpetuate the conditions for life on the planet. The hypothesis was formulated by the chemist James Lovelock and co-developed by the microbiologist Lynn Margulis in the 1970s. Lovelock named the idea after Gaia, the primordial goddess who personified the Earth in Greek mythology. The suggestion that the theory should be called "the Gaia hypothesis" came from Lovelock's neighbour, William Golding. In 2006, the Geological Society of London awarded Lovelock the Wollaston Medal in part for his work on the Gaia hypothesis. Topics related to the hypothesis include how the biosphere and the evolution of organisms affect the stability of global temperature, salinity of seawater, atmospheric oxygen levels, the maintenance of a hydrosphere of liquid water and other environmental variables that affect the habitability of Earth. The Gaia hypothesis was initially criticized for being teleological and against the principles of natural selection, but later refinements aligned the Gaia hypothesis with ideas from fields such as Earth system science, biogeochemistry and systems ecology. Even so, the Gaia hypothesis continues to attract criticism, and today many scientists consider it to be only weakly supported by, or at odds with, the available evidence.
  • 6.6K
  • 07 Nov 2022
Topic Review
Central Nervous System in Autism Spectrum Disorder
Autism spectrum disorder (ASD) is a heterogeneous, behaviorally defined, neurodevelopmental disorder that has been modeled as a brain-based disease.
  • 6.6K
  • 20 Jan 2022
Topic Review Peer Reviewed
Solar Chimney Applications in Buildings
A solar chimney is a renewable energy system used to enhance the natural ventilation in a building based on solar and wind energy. It is one of the most representative solar-assisted passive ventilation systems attached to the building envelope. It performs exceptionally in enhancing natural ventilation and improving thermal comfort under certain climate conditions. The ventilation enhancement of solar chimneys has been widely studied numerically and experimentally. The assessment of solar chimney systems based on buoyancy ventilation relies heavily on the natural environment, experimental environment, and performance prediction methods, bringing great difficulties to quantitative analysis and parameterization research. With the increase in volume and complexity of modern building structures, current studies of solar chimneys have not yet obtained a unified design strategy and corresponding guidance. Meanwhile, combining a solar chimney with other passive ventilation systems has attracted much attention. The solar chimney-based integrated passive-assisted ventilation systems prolong the service life of an independent system and strengthen the ventilation ability for indoor cooling and heating. However, the progress is still slow regarding expanded applications and related research of solar chimneys in large volume and multi-layer buildings, and contradictory conclusions appear due to the inherent complexity of the system.
  • 6.6K
  • 13 Apr 2022
Topic Review
Design Challenges and Limitations of Injectable Hydrogels
Injectable hydrogels (IHs) are smart biomaterials and are the most widely investigated and versatile technologies, which can be either implanted or inserted into living bodies with minimal invasion. Their unique features, tunable structure and stimuli-responsive biodegradation properties make these IHs promising in many biomedical applications, including tissue engineering, regenerative medicines, implants, drug/protein/gene delivery, cancer treatment, aesthetic corrections and spinal fusions. Regarding their current prospective and ongoing research, hydrogel formulations have some limitations in their applications, clinical practices and sustainability. Many hydrogel systems (natural/synthetic), such as thermosensitive hydrogels, are free-flowing sols at a low temperature, while upon raising to body temperature (physiological temperature), they are converted to a stable visco-elastic gel phase, such as poly (phosphazene), pluronic and poly (N-isopropyl acrylamide). 
  • 6.6K
  • 08 Apr 2022
Topic Review
Lithium-Ion Battery Fire Suppression
Lithium-ion Batteries (LiBs) hazards, techniques for mitigating risks, the suppression of LiB fires and identification of shortcomings for future improvement were thoroughly reviewed. Water is identified as an efficient cooling and suppressing agent and water mist is considered the most promising technique to extinguish LiBs fire. 
  • 6.6K
  • 29 Apr 2021
Topic Review
Herfindahl–Hirschman Index
The Herfindahl index (also known as Herfindahl–Hirschman Index, HHI, or sometimes HHI-score) is a measure of the size of firms in relation to the industry they are in and an indicator of the amount of competition among them. Named after economists Orris C. Herfindahl and Albert O. Hirschman, it is an economic concept widely applied in competition law, antitrust and also technology management. HHI is calculated by squaring the market share of each competing firm in the industry and then summing the resulting numbers,(sometimes limited to the 50 largest firms), where the market shares are expressed as fractions or points. The result is proportional to the average market share, weighted by market share. As such, it can range from 0 to 1.0, moving from a huge number of very small firms to a single monopolistic producer. Increases in the Herfindahl index generally indicate a decrease in competition and an increase of market power, whereas decreases indicate the opposite. Alternatively, if whole percentages are used, the index ranges from 0 to 10,000 "points". For example, an index of .25 is the same as 2,500 points. The major benefit of the Herfindahl index in relationship to such measures as the concentration ratio is that it gives more weight to larger firms. Other benefits of the Herfindahl index includes its simple calculation method and the small amount of easily obtainable data required for the calculation. The measure is essentially equivalent to the Simpson diversity index, which is a diversity index used in ecology; the inverse participation ratio (IPR) in physics; and the effective number of parties index in politics.
  • 6.6K
  • 24 Oct 2022
Topic Review
Communication
Communication (from Latin communicare, meaning "to share"or "to be in relation with") is "an apparent answer to the painful divisions between self and other, private and public, and inner thought and outer word." As this definition indicates, communication is difficult to define in a consistent manner, because it is commonly used to refer to a wide range of different behaviors (broadly: "the transfer of information"), or to limit what can be included in the category of communication (for example, requiring a "conscious intent" to persuade). John Peters argues the difficulty of defining communication emerges from the fact that communication is both a universal phenomena (because everyone communicates), and a specific discipline of institutional academic study. One possible definition of communication is the act of developing meaning among entities or groups through the use of sufficiently mutually understood signs, symbols, and semiotic conventions. In Claude Shannon's and Warren Weaver's influential model, human communication was imagined to function like a telephone or telegraph. Accordingly, they conceptualized communication as involving discrete steps: These elements are now understood to be substantially overlapping and recursive activities rather than steps in a sequence. For example, communicative actions can commence before a communicator formulates a conscious attempt to do so, as in the case of phatics; likewise, communicators modify their intentions and formulations of a message in response to real-time feedback (e.g., a change in facial expression). Practices of decoding and interpretation are culturally enacted, not just by individuals (genre conventions, for instance, trigger anticipatory expectations for how a message is to be received), and receivers of any message operationalize their own frames of reference in interpretation. The scientific study of communication can be divided into: The channel of communication can be visual, auditory, tactile/haptic (e.g. Braille or other physical means), olfactory, electromagnetic, or biochemical. Human communication is unique for its extensive use of abstract language. Development of civilization has been closely linked with progress in telecommunication.
  • 6.6K
  • 02 Nov 2022
Topic Review
Chemistry in Health Care
The importance of chemistry in nursing is evident in every aspect of patient care. From understanding drug interactions and diagnostic tools to interpreting biochemical data and embracing innovative technologies.
  • 6.6K
  • 31 Oct 2024
Topic Review
Biodiesel Production from Animal Fats Versus Vegetable Oils
Biodiesel, a mixture of fatty acids alkyl esters shows properties, which make it a feasible substitute for fossil diesel. Biodiesel can be produced using different processes and different raw materials. The most common, first generation, biodiesel is produced by methanolysis of vegetable oils using basic or acid homogeneous catalysts. The use of vegetable oils for biodiesel production raises serious questions about biodiesel sustainability. Used cooking oils and animal fats can replace the vegetable oils in biodiesel production thus allowing to produce a more sustainable biofuel. 
  • 6.6K
  • 19 Jan 2024
Topic Review
Bureaucracy
Bureaucracy is a concept that refers to a formal organizational structure characterized by a hierarchical arrangement of tasks, authority, and responsibilities. Rooted in the principles of efficiency, rationality, and specialization, bureaucracy represents a system of administration designed to streamline decision-making processes, facilitate coordination, and ensure the efficient functioning of complex organizations. The term is often associated with administrative entities, government agencies, and large corporations, where intricate tasks require systematic management.
  • 6.6K
  • 25 Jan 2024
Biography
Guru Nanak
Gurū Nānak (15 April 1469 – 22 September 1539), also referred to as Bābā Nānak ('father Nānak'),[1] was the founder of Sikhism and is the first of the ten Sikh Gurus. His birth is celebrated worldwide as Guru Nanak Gurpurab on Katak Pooranmashi ('full-moon of Kattak'), i.e. October–November. Nanak is said to have travelled far and wide across Asia teaching people the message of ik onk
  • 6.6K
  • 09 Dec 2022
Topic Review
Traditional Chinese Timekeeping
The traditional Chinese time systems refers to the time standards for divisions of the day used in China until the introduction of the Shixian calendar in 1628 at the beginning of the Qing dynasty.
  • 6.6K
  • 30 Oct 2022
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