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Topic Review
The Spemann Organizer
In 1924, to understand the processes involved in developmental biology, Spemann and Mangold transplanted a blastopore lip between different ectodermal regions of amphibian embryos. The transplanted dorsal tissue differentiated mostly into a notochord, while the ectoderm of the host dorsal tissue that was sitting above the transplanted region (blastopore lip) was induced and differentiated to form a Siamese twin containing dorsal tissues such as somites and a neural plate, which would form the central nervous system, forming the bulk of a second axis. The major findings were that the transplant had altered the fate of the overlying cells and that the neural folds were built from recipient cells and not donor cells. Spemann and Mangold discovered the organizing center in the dorsal blastopore lip of amphibians. This center consists of a cluster of cells in the developing embryo that have the ability to interact and instruct morphogenesis in the surrounding cells during gastrulation. When transplanted to the ventral side of the embryo, the center will induce the formation of a secondary axis, promoting the development of the central nervous system, organs, and tissues, as well as the formation of the main body axis. Spemann and Mangold found the first evidence of the organizing center, thereafter called the “Spemann organizer”, and its major role in the development of vertebrates. This discovery also introduced the concept of induction in embryonic development, which refers to the method used by specific cells to affect the fate of other embryonic cells. A major milestone had been achieved for developmental biology.
  • 2.5K
  • 11 Nov 2021
Topic Review
Gade Language in Nigeria
History of Gade Language in Nigeria and the Africa 
  • 2.5K
  • 28 Oct 2020
Topic Review
HRM–CSR–SP Relationship
Human Resource Management–Corporate Social Responsibility–Sustainable Performance (HRM–CSR–SP) relationship is considered as a strong theoretical foundation where HRM is critical in educating firms on the values of CSR and leading behaviors to pursue a sustainable performance. This relationship explains the organizations’ behaviors towards developing and implementing CSR policies into strategic and operational decisions by engaging their employees supported by HRM practices to achieve sustainable performance (social, environmental, financial performance).
  • 2.5K
  • 17 Jan 2022
Topic Review
Coherence
In physics, two wave sources are coherent if their frequency and waveform are identical. Coherence is an ideal property of waves that enables stationary (i.e. temporally or spatially constant) interference. It contains several distinct concepts, which are limiting cases that never quite occur in reality but allow an understanding of the physics of waves, and has become a very important concept in quantum physics. More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets. Interference is the addition, in the mathematical sense, of wave functions. A single wave can interfere with itself, but this is still an addition of two waves (see Young's slits experiment). Constructive or destructive interference are limit cases, and two waves always interfere, even if the result of the addition is complicated or not remarkable. When interfering, two waves can add together to create a wave of greater amplitude than either one (constructive interference) or subtract from each other to create a wave of lesser amplitude than either one (destructive interference), depending on their relative phase. Two waves are said to be coherent if they have a constant relative phase. The amount of coherence can readily be measured by the interference visibility, which looks at the size of the interference fringes relative to the input waves (as the phase offset is varied); a precise mathematical definition of the degree of coherence is given by means of correlation functions. Spatial coherence describes the correlation (or predictable relationship) between waves at different points in space, either lateral or longitudinal. Temporal coherence describes the correlation between waves observed at different moments in time. Both are observed in the Michelson–Morley experiment and Young's interference experiment. Once the fringes are obtained in the Michelson interferometer, when one of the mirrors is moved away gradually from the beam-splitter, the time for the beam to travel increases and the fringes become dull and finally disappear, showing temporal coherence. Similarly, in a double-slit experiment, if the space between the two slits is increased, the coherence dies gradually and finally the fringes disappear, showing spatial coherence. In both cases, the fringe amplitude slowly disappears, as the path difference increases past the coherence length.
  • 2.5K
  • 16 Nov 2022
Topic Review
Procedures for Extraction of Anthocyanins from Different Food
Anthocyanins are water-soluble pigments characterized by various intense colors found in fruits and vegetables. The extraction and separation of anthocyanins from plants is important, especially due to the instability of plant anthocyanins, selecting and optimizing. Anthocyanins are prone to degradation by several factors, including pH, temperature, oxygen, water activity, co-pigments and enzymes. Unwanted compounds, such as sugars, proteins, lipids, acids and other flavonoids, can also be removed from plant material by appropriate extraction methods. The most used method for anthocyanin extraction is the conventional one, solid–liquid extraction, also known as solvent extraction, during which anthocyanins can be dissolved in polar solvents (methanol/glycolic acid and acetone), followed by their quantification, achieved by using spectrophotometry, the differential pH method, which is a rapid and convenient quantitative assay. Starting from this point, it has developed and there are many anthocyanin-extraction methods, such as conventional solvent extraction (CSE), enzyme-assisted extraction (EAE), fermentation extraction (FE), supercritical fluid extraction (SFE) (CO2) extraction, microwave-assisted extraction (MAE), ultrasonic-assisted extraction (UAE), high-hydrostatic-pressure extraction (HHPE) and pressurized-liquid extraction (PLE). One of the most frequent techniques for obtaining anthocyanins from plants is conventional solvent extraction. In order to meet the demands of safety and environmental sustainability, new extraction technologies with shorter extraction periods and higher yields have been developed (e.g., PLE, EFS, UAE, MAE, EAE, etc.).
  • 2.5K
  • 29 Nov 2022
Topic Review
Climate Change Maladaptation
Maladaptation is caused by adaptation that fails to reduce vulnerability or inadvertently increases it. Maladaptation can be defined as: ''maladaptation occurs when short-term strategies increase vulnerability in the long term'' or ''action taken ostensibly to avoid or reduce vulnerability to climate change that impacts adversely on, or increase the vulnerability of other systems, sectors, or social groups.''
  • 2.5K
  • 29 Mar 2021
Topic Review
Impacts of Agroforestry on Rural Communities
Agroforestry can be used as an alternative way to tackle ecological crisis, while at the same time, sustaining crop production. This system integrates tree growing and crop cultivation and/or animal production on the same land management, based on spatial arrangement or temporal sequence. With such tree integration, agroforestry can preserve natural ecosystems through sustainable land management (including reforestation) and optimal resource utilization. Moreover, agroforestry can potentially mitigate climate change, as several practices within the system are found to improve carbon sequestration and therefore reducing greenhouse gas (GHG) emissions. Moreover, the system can promote biodiversity through the incorporation of different species of plants/crops which may provide homes for various wildlife. Apart from its positive impact on the environment, several studies have also highlighted the socio-economic benefits of agroforestry for rural communities. The implementation of a diverse agroecosystem including trees (timbers, fruits) and livestock might provide alternative incomes for the community promoting economic resilience. Furthermore, the system might improve household food security through diversified food sources. Thus, agroforestry might also become a solution for the existing socio-economic issues.
  • 2.5K
  • 14 Apr 2022
Topic Review
Mercedes-Benz CLA-Class
The Mercedes-Benz CLA class is a series of luxury compact executive cars manufactured by Mercedes-Benz since 2013. The first generation was a four-door sedan based on the platform of the W176 A-Class and W246 B-Class compact cars, marketed as a four-door coupé. In 2015, Mercedes-Benz expanded the CLA family to include the Shooting Brake, a station wagon configuration. As the V177 A-Class sedan took its place as the budget-conscious sedan, the second generation got longer and wider than the W205 C-Class. The CLA is Mercedes-Benz's first front-wheel drive vehicle offered in the North American market. The CLA range is positioned above the A-Class and it is nearly on the level of the C-Class in the Mercedes model range, and models tend to be less practical than the A-Class it is based on. The CLA first went on sale in Europe in April 2013, and was subsequently introduced in the United States in September 2013. Its largest markets are Western Europe and the United States. Global cumulative CLA sales reached 100,000 during its first year, cited as "our best launch in 20 years" by Mercedes-Benz. Worldwide, Mercedes-Benz sold about 750,000 units of the first generation.
  • 2.5K
  • 28 Oct 2022
Topic Review
Dog-Whistle Politics
Dog-whistle politics is the use of coded or suggestive language in politics to garner support from a wider audience for a candidate. Dog whistles serve the purpose of attracting the intended political audience without garnering ire with opposing audiences, similar to ultrasonic dog whistles used in sheepherding. The concept of dog-whistles has similarities to the concept of code words. Accusations of dog-whistling may be used to accuse an individual of expressing a "hidden" meaning when no such message was intended and the actual words used are innocuous. Such accusations can be a form of political correctness or gaslighting and are by their nature impossible to refute. An example is the accusation that using the phrase "international banks" is evidence of anti-Semitism. When it exists, a dog-whistle is a type of doublespeak used in political messaging. Dog whistles work by employing language that has normal meanings to the majority, but can be implied or loaded to mean very specific things to intended recipients. One example commonly believed to be dog whistling may include is the use of 'family values' as a signal to Christians that the candidate is Christian and would support policies related to Christian values without raising flags among the non-religious who might oppose a Christian candidate. This type of dog whistle would serve the purpose of gaining popularity with Christians without losing popularity with non-Christians.
  • 2.5K
  • 25 Nov 2022
Topic Review
Anno Mundi
Anno Mundi (Latin for "in the year of the world"; Hebrew: לבריאת העולם, "to the creation of the world"), abbreviated as AM, or Year After Creation, is a calendar era based on the biblical accounts of the creation of the world and subsequent history. Two such calendar eras have seen notable use historically: While differences in biblical interpretation or in calculation methodology can produce some differences in the creation date, most results fall relatively close to one of these two dominant models. The primary reason for the disparity seems to lie in which underlying Biblical text is chosen (roughly 5500 BC based on the Greek Septuagint text, about 3750 BC based on the Hebrew Masoretic text). Most of the 1,732-year difference resides in numerical discrepancies in the genealogies of the two versions of the Book of Genesis. Patriarchs from Adam to Terah, the father of Abraham, are said to be older by as much as 100 years or more when they begat their named son in the Greek Septuagint than they were in the Latin Vulgate (Genesis 5; Genesis 11) or the Hebrew Tanakh (Gen 5; Gen 11). The net difference between the two major genealogies of Genesis is 1466 years (ignoring the "second year after the flood" ambiguity), 85% of the total difference. (See Dating creation.)
  • 2.5K
  • 03 Nov 2022
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